Chronic actions of thyroxine on behavior and serotonin receptors in mouse strains with contrasting predispositions to catalepsy.

The studies reported here addressed the effects of chronic administration of thyroxine (2 mg/liter for 60 days) on catalepsy and the functional activity and expression of the 5-HT(1A) and 5-HT(2A) receptor genes in the brains of adult male mice of the cataleptic ASC strain and the catalepsy-resistant AKR strain. Thyroxine induced cataleptics in AKR mice but had anticataleptic activity in ASC animals. Chronic thyroxine administration increased the functional activity and expression of 5-HT(2A) receptors in the frontal cortex in AKR mice but not in ASC mice. In ASC mice, the hormone significantly weakened the hypothermic effect of the 5-HT(1A) receptor agonist 8-OH-DPAT, though it did not alter the expression of these receptors. These results suggest that 5-HT(2A) receptors are involved in the cataleptogenic while 5-HT(1A) receptors are involved in the anticataleptic effects of the hormone in mice.